Gaseous hydrocarbons, particularly propane, are used as coolant to protect nozzles for and bottoms of vessels used in processes, such as those employed for refining pig iron. Liquid hydrocarbons are alternatively added through jackets of jacketed nozzles through which oxygen is introduced into the melt.
Thus introduced hydrocarbons, which are blown into molten metal (in addition to oxygen) have a cooling effect because of their thermal decomposition, and they serve as protection for the nozzles and the floor or base of the refining vessel, e.g. converter.
In such processes a major portion of hydrogen (produced by hydrocarbon decomposition) passes through the metal bath almost completely uncombusted, so that little heat is developed from the added amount of hydrocarbon; moreover, the hydrocarbon decomposition is endothermal. In addition, the liquid steel absorbs hydrogen which must be subsequently removed by a costly cleaning process, for example by rinsing with suitable gas.
When partially or completely uncombusted waste gas is extracted to permit purification of the waste gas and thus keep the cost low, a further serious drawback results; the hydrogen content of the waste gas increases the danger of explosion in the waste gas system when it exceeds certain limits. For this reason, enlargement of the hydrocarbon stream, for example for the purpose of turning over larger quantities of scrap metal, is narrowly confined.
A method for air refining with pure oxygen (German Patent No. 763,185) provides introduction into a converter of gaseous, liquid or, preferably, solid additives, such as carbon dust, by means of separately introduced compressed air by blowing these materials through nozzles in the bottom usually employed in bottom blowing converters. This process cannot be used for blowing with more or less pure oxygen because the carbon would be ignited shortly before it leaves the nozzles and the firing points in the nozzle would move downwardly, thus destroying the nozzle bottom.